Comments on: How much gas does starting the car use?

Question: How much gas does starting the car use?

SwingingJohnson1968 — Mon, 30 Jan 2006 16:10:52 -0800

Do I waste more gas by letting the car idle for 5 minutes or by turning off and restarting?

I always heard that starting the car uses alot of fuel.

By: disillusioned

disillusioned — Mon, 30 Jan 2006 16:13:40 -0800

4. Minimise fuel wasted in idling

Minimise fuel wasted in idling by stopping the engine whenever your car is stopped or held up for an extended period of time. By having the engine switched off, even for a short period, you will save more fuel than is lost from the burst of fuel involved in restarting the engine. The net increased wear and tear from this practice is negligible.

(Source. But it's the Australian government. No figures to back it up, natch.)

By: stray

stray — Mon, 30 Jan 2006 16:14:53 -0800

Idling for just 10 seconds uses more fuel than restarting an engine and actually causes more engine wear, according to this site. Googling "car idle 10 seconds" brings up many similar results.

By: tiamat

tiamat — Mon, 30 Jan 2006 16:22:52 -0800

I'm told this *used* to be the case - but now cars start more efficiently, making the first two comments correct.

By: delmoi

delmoi — Mon, 30 Jan 2006 16:28:28 -0800

You do if you have a prius or Honda hybrid.

By: Civil_Disobedient

Civil_Disobedient — Mon, 30 Jan 2006 16:33:43 -0800

There are a couple of schools of thought.

The first says that it's a pretty even tradeoff between cost of fuel and cost of engine wear. Figure if you turned your car on and off like that every day all winter, you'll probably knock a few thousand miles off the final odometer reading before a rebuild. So either idle and pay for it now, or pay for it later when you have to get a new (whatever). That's fine when gas is only fifty cents a gallon.

Nowadays I'm not so sure. Car engines are engineered really tight these days, and every spare scrap of fuel economy is being wrung out of increasingly expensive gas. I'd say a properly maintained modern engine (provided you changed the oil like a good car owner should) will last you three or four hundred thousand miles--that's a shitload of idling over time and gas isn't getting any cheaper, so you're better off turning the car off.

By: ontic

ontic — Mon, 30 Jan 2006 16:34:26 -0800

Click and Clack on saving gas by idling as opposed to stopping and restarting: "It's complete B.S."

Modern starters can more than handle the wear-and-tear from shutting off and restarting frequently and it takes little to no gas.

By: smackfu

smackfu — Mon, 30 Jan 2006 16:34:58 -0800

you will save more fuel than is lost from the burst of fuel involved in restarting the engine

Well, not to criticize the Australians, but I would think that you'd also have to use some gas to top the battery back up, since the starter puts a heavy load on it to turn the engine over.

By: wilful

wilful — Mon, 30 Jan 2006 16:35:48 -0800

Electronic fuel injection and electronic chokes means that it's a thing of the past. You would use more fuel for a couple of seconds at most. At the lights, turn your car off if you're confident you can restart it in time.

Note how hybrids often turn their petrol engines off when stopped these days?

By: Meredith

Meredith — Mon, 30 Jan 2006 16:41:16 -0800

I drive a Honda Civic Hybrid and this is one of the ways it is designed to economize fuel. When I come to a stop the engine automatically shuts off, and stays off until I take my foot off the brake.

By: hangashore

hangashore — Mon, 30 Jan 2006 16:47:52 -0800

Also have a gander at this related recent thread.

By: kimota

kimota — Mon, 30 Jan 2006 17:25:58 -0800

Just to clarify, when discussing cars, does "modern" mean 'since 1995', 'since 2000', or what?

By: kindall

kindall — Mon, 30 Jan 2006 17:54:55 -0800

when discussing cars, does "modern" mean 'since 1995', 'since 2000', or what?

In this particular discussion I would say it includes any car with fuel injection.

By: tcobretti

tcobretti — Mon, 30 Jan 2006 19:27:13 -0800

I feel like I should point out that I have changed a lot of starters in my day. In my home town there is a prospering business whose entire purpose is rebuilding starters and alternators.

I do think that starter failure has as much to do with chronological age as it has to do with use, though.

The real way to solve this question is buy a car with a standard transmission and push start it all the time; that way no emissions (when it's turned off, anyway) AND no problems with broken starters.

By: five fresh fish

five fresh fish — Mon, 30 Jan 2006 19:29:25 -0800

At the lights, turn your car off if you're confident you can restart it in time.

An exceedingly poor idea in terms of accident risk control.

With the engine running you have many more options available to you when faced with an oncoming accident situation.

You shall want to evaluate the reduced mobility and control options, before deciding that being parked dead-engine in the middle of traffic is a good idea. I should imagine the answer is highly situationally-dependent.

By: Dasein

Dasein — Mon, 30 Jan 2006 21:28:45 -0800

There are a couple of schools of thought.

And one of these schools is wrong. As tiamat said, it used to take more gas to start a car than to let it idle for a while, but not anymore. Mercedes actually did a demonstration at a car show about six years ago (maybe more) where they turned a car on and off repeatedly for a minute, measuring gas usage precisely, to demonstrate that it takes more gas to idle the engine than to start up your car again.

By: Civil_Disobedient

Civil_Disobedient — Mon, 30 Jan 2006 23:45:56 -0800

Along 5ff's line of thinking: if you kill the power, you kill your power brakes. That's no good.

By: Civil_Disobedient

Civil_Disobedient — Mon, 30 Jan 2006 23:48:11 -0800

Also, on (non) preview:

to demonstrate that it takes more gas to idle the engine than to start up your car again

While that was what the OP asked, the first point I made was comparing your overall costs, not gas costs specifically.

By: funambulist

funambulist — Tue, 31 Jan 2006 02:24:36 -0800

As has already been said, yes, you do waste more, and 5 minutes sounds like a lot to leave the car idle.

Definitely do *not* turn it off at the lights though - you're asking to be bumped, or at least piss off the drivers behind you being held as you restart the car.

By: furtive

furtive — Tue, 31 Jan 2006 07:31:40 -0800

Our local paper had an article on this recently and amongst the other facts it said that you should shut off the engine for any idling longer than 30 seconds.

By: armage

armage — Tue, 31 Jan 2006 07:58:53 -0800

For what it's worth diesel-powered buses here in Tokyo cut their engines when they come to traffic signals.

By: Mitheral

Mitheral — Tue, 31 Jan 2006 08:36:21 -0800

tiamat writes "I'm told this *used* to be the case"

Pre electrically controlled carbs (and later electronic fuel injection) there wasn't much feedback to the carb whether the engine needed cold start enrichment or not. Considering that the consequence of no enrichment when needed (no start) is much worse than enrichment when warm (momentary rough idle and wasted gas) manufacturers of course went with wasting gas. The enichment pumps on a 800CFM four barrel will move an amazing amount of gas, wildly more so than the same carb at idle at full vacuum.

Civil_Disobedient writes "Along 5ff's line of thinking: if you kill the power, you kill your power brakes. That's no good."

All brake boosters have at least one hard stop of reserve capacity when the engine has been recently running.

By: nomisxid

nomisxid — Tue, 31 Jan 2006 10:18:30 -0800

In Seattle, all the drawbridge approaches have signs warning motorists to turn off the car when waiting for the bridge.

Note, that turning your car off at every intersection might be illegal in many states. I know it's illegal to have the engine running, but be in neutral/park at the light, specifically because of the safety issues mentioned above by others....

By: Civil_Disobedient

Civil_Disobedient — Tue, 31 Jan 2006 18:06:17 -0800

All brake boosters have at least one hard stop of reserve capacity when the engine has been recently running.

Unfortunately most drivers will be riding their brakes and releasing a lot of that built-up pressure before they realize what's going on. I personally would be annoyed to have to stand on my breaks. If I wanted to exercise I wouldn't be driving.

By: Civil_Disobedient

Civil_Disobedient — Tue, 31 Jan 2006 18:06:52 -0800

Freudian typo:

my brakes, not breaks.

By: five fresh fish

five fresh fish — Wed, 01 Feb 2006 09:30:10 -0800

The brakes are the least of the problem: without the engine running your power-assisted steering is going to be a bear to operate and -- just as importantly -- you can't accelerate.

The acceleration bit should not be underestimated: the ability to move even a few feet forward could make the difference between a costly rear-ending, and no rear-ending.